A French-Vietnamese maths professor has been sentenced to three years in a Vietnamese prison for belonging to a banned pro-democracy group and publishing an anti-communist blog, his lawyer said.

Pham Minh Hoang, 56, was found guilty of trying to overthrow the government by posting 33 articles against the one-party communist government, as well as of holding membership in the banned Viet Tan group and recruiting others to join it. It was the second high-profile dissident trial in just over a week.

US-based Viet Tan says it is a nonviolent advocate of democracy, but Hanoi considers it a terror organisation – a claim US officials say they have found no evidence to support.

Hoang told the court during the half-day trial in Ho Chi Minh City that he joined Viet Tan in France where it is not banned and that he did not do anything to oppose the government, according to defence lawyer Tran Vu Hai.

Hoang, who was teaching maths at a Ho Chi Minh City university at the time of his arrest, said he returned to Vietnam in 2000 to contribute to the country and take care of his ailing parents, Hai said.

The court convicted him on charges that included attending a Viet Tan-organised course in Malaysia and helping to recruit Vietnamese members, Hai said.

The communist government does not tolerate dissent, and rights groups say it uses vague national security laws to imprison anyone who challenges its rule. Hanoi maintains that only lawbreakers are jailed, but there has been a wave of crackdowns since the country's new government took over last month.

Last week, an appeals court in Hanoi upheld a seven-year prison sentence for the dissident son of one of Vietnam's founding revolutionaries, despite arguments that his support for a multiparty system did not mean he was against the Communist party.

The ruling against Cu Huy Ha Vu drew immediate criticism from activists, the US government and the European Union.

The Communist party newspaper Nhan Dan quoted foreign ministry spokeswoman Nguyen Phuong Nga as saying Hanoi rejected what it called "statements that interfere with its internal affairs."

Two weeks ago the US also called for the release of one of Vietnam's best-known pro-democracy activists, a Roman Catholic priest suffering from a brain tumour. The Rev Thadeus Nguyen Van Ly, 65, was sent back to prison after receiving more than a year of medical leave.